Among petroleum products, for example, lube-oils, gas oils and jet fuels are products whose cold flow property is given importance to. Therefore, base oils used in these products are desirably ones from which wax components such as normal paraffins and slightly branched isoparaffins causing reduction of cold flow property are completely or partially removed, or in which the wax components are converted to components other than the wax components. Hydrocarbons obtained by Fischer-Tropsch synthesis method are recently paid attention as feedstock oils when lube-oils and fuels are manufactured in view of containing no environmental load substances such as sulfur compounds, but the hydrocarbons also contain many wax components.
As a dewaxing technology to remove wax components from hydrocarbon oils, for example, a method of extracting wax components with a solvent such as liquefied propane or MEK is known. However, this method has such problems that the operational cost is high, the applicable kind of feedstock oil is limited, and further, the product yield is limited by the kind of feedstock oil.
On the other hand, as a dewaxing technology to convert wax components in hydrocarbon oils to non-wax components, for example, catalytic dewaxing is known by which the hydrocarbon oil is brought into contact with a so-called bifunctional catalyst having a hydrogenation-dehydrogenation capability and an isomerization capability to isomerize normal paraffins in the hydrocarbon to isoparaffins. As bifunctional catalysts used for catalytic dewaxing, solid acids, particularly catalysts containing a molecular sieve composed of zeolite or the like and a metal of Group 8 to 10, or 6 of Periodic Table of the elements, especially catalysts in which the molecular sieve carries the metal, are known.
The catalytic dewaxing is effective as a method of improving the cold flow property of hydrocarbon oils, but to obtain fractions suitable for lube-oil base oils and fuel base oils, the conversion of normal paraffins must be sufficiently high. However, since the catalysts used in the catalytic dewaxing have an isomerization capability and also a cracking capability of hydrocarbons, in the case where hydrocarbon oils are catalytically dewaxed, a rise in the conversion of the normal paraffins involves progress of turning the hydrocarbon oils into light oils, bringing about a difficulty of obtaining desired fractions with a high yield. Especially in the case where base oils for high-quality lube-oils required to have a high viscosity index and a low pour point are manufactured, it is very difficult to economically obtain target fractions by catalytic dewaxing of hydrocarbon oils, and therefore, synthetic base oils such as poly-α-olefins are often used in such a field.
From the above situations, in the field of manufacturing lube-oil base oils and fuel base oils, a catalytic dewaxing technology to obtain desired isoparaffin fractions from hydrocarbon oils containing wax components with a high yield is demanded.
Attempts have been made so far to improve the isomerization selectivity of catalysts used in the catalytic dewaxing. For example, Patent Document 1 described below discloses a process to manufacture a dewaxed lube-oil by bringing a raw material of a straight-chain or slightly branched hydrocarbon having 10 or more carbon atoms into contact with a catalyst composed of a molecular sieve which has medium-sized one-dimensional pores such as ZSM-22, ZSM-23 and ZSM-48 containing a metal of Group VIII or the like in Periodic Table and whose crystallites have a size not exceeding about 0.5 μm, under an isomerization condition.
A molecular sieve constituting a catalyst for catalytic dewaxing is usually manufactured by hydrothermal synthesis in the presence of an organic template containing an amino group, an ammonium group or the like to establish a predetermined pore structure. Then, the synthesized molecular sieve is calcined at a temperature of, for example, about 550° C. or higher in an atmosphere containing molecular oxygen to remove the contained organic template, for example, as described in the final paragraph in section “2.1. Materials” on page 453 of Non-Patent Document 1 shown below. Next, the calcined molecular sieve is typically ion-exchanged into an ammonium type in an aqueous solution containing ammonium ions, for example, as described in section “2.3. Catalytic experiments” on page 453 of Non-Patent Document 1. On the molecular sieve after the ion-exchange, a metal component of Groups 8 to 10 or the like in Periodic Table of the elements is further carried. Then, the molecular sieve on which the metal component is carried is dried, and filled in a reactor, optionally through a process such as molding, and calcined typically at a temperature of about 400° C. in an atmosphere containing molecular oxygen, and further subjected to a reduction treatment using hydrogen or the like at about the same temperature to impart a catalytic activity as a bifunctional catalyst.    [Patent Document 1] U.S. Pat. No. 5,282,958    [Non-Patent Document 1] J. A. Martens, et. al., J. Catal., 2006, 239, 451